Nineteen fungal strains associated with the seagrass Posidonia oceanica, with the green alga Flabellia petiolata, and the brown alga Padina pavonica were collected in the Mediterranean Sea. These strains were previously identified at the family level and hypothesised to be undescribed species. Strains were examined by deep multi-loci phylogenetic and morphological analyses. Maximum-likelihood and Bayesian phylogenies proved that Parathyridariella gen. nov. is a distinct genus in the family Thyriadriaceae. Analyses based on five genetic markers revealed seven new species: Neoroussoella lignicola sp. nov., Roussoella margidorensis sp. nov., R. mediterranea sp. nov., and R. padinae sp. nov. within the family Roussellaceae, and Parathyridaria flabelliae sp. nov., P. tyrrhenica sp. nov., and Parathyridariella dematiacea gen. nov. et sp. nov. within the family Thyridariaceae.